Artificially raised nitrate concentrations of seawater decreased rapidly to the naturally low concentrations when the water was in contact with the surface of the Wadden Sea sediment. Ammonia was released attaining final stable concentrations. A state of balance between the community activity of the sediment and concentrations in the layer of water over the sediment is assumed, which has to be modulated in order to observe efflux and influx (as process restoring balance)